Elemental sulfur is an attractive cathode material for lithium batteries because of its high theoretical capacity (1672 mAh/g) and specific energy (2600 Wh/kg), assuming complete reaction of lithium with sulfur to form Li2S. It also has the advantage of relatively low cost and environmental impact as an electrode material. Practical realization of an acceptable Li—S battery is a challenge for at least two reasons. Elemental sulfur, and its discharge products, has a highly electrically insulating nature (5×10−30 S cm−1 at 25° C.), which can lower both electrochemical activity and the utilization ratio of sulfur. Another issue commonly associated with the Li—S system is poor cyclability caused by the high solubility of the intermediate lithium polysulfide, Li2Sx (2≤x≤8), formed during both charge and discharge processes. Dissolved polysulfides can diffuse to the lithium anode where they are then subsequently reduced to short chain polysulfides. Those soluble species can also transport back to the cathode and be reoxidized into long chain polysulfides. The above parasitic process creates an internal shuttle reaction, which results in low coulombic efficiency. Moreover, a fraction of the soluble polysulfides are strongly reduced into insoluble Li2S2 and/or Li2S, which are then deposited on the anode surface and gradually form a thick layer upon repeated cycling. The same phenomenon also occurs on the cathode surface during discharge. The deactivated insoluble agglomerates on both electrodes can lead to a progressive loss of active materials, inaccessibility of the active components in the interior sulfur electrode, a serious morphology change of the electrode, and increased cell impedance. These cumulative effects can then be reflected in a rapid capacity degradation of the Li—S battery upon charge/discharge cycling.
In order to address the aforementioned challenges, a matrix can be designed to not only support good conductivity and dispersion of sulfur, but also, to constrain sulfur and the polysulfides within a framework. However, simple physical confinement and/or sorption does not appear to be sufficiently effective in retarding polysulfide dissolution so as to improve cycle life. Accordingly, a need exists for an improved composite material exhibiting high capacity retention and high charge/discharge cycle stability when utilized as an electrode in Li—S energy storage devices.